Tuning or sensor issue?

Here's the skinny. I rebuilt my LS this winter and threw a Brian Tooley cam in it while I was at it. Before all this, I was running a speed density tune with no issues whatsoever. I was anticipating re-tuning, but utilizing a closed loop tune this time around. However, I can't even get the car to idle, which is weird for three reasons. 1., the cam isn't that big, 2. the tune I have runs a little rich anyway for the track and 3. the first two times I started it the engine idled fine. Tonight I double checked all the connections and cleaned them, but still no dice.

So the question still stand, tuning or sensor issue?

one thing i learned about with tuning for an aftermarket cam is to change your stoich air/fuel ratio to 14.0 or even 13.5. with a big cam at idle the o2 sensors can pick up a false rich and the pcm tries to lean it out. it likely ran fine the first couple times because the fuel trims hadnt had a chance to work themselves too far out of wack.

That would make sense, but i currently have an open loop speed density tune, so the O2's aren't active.

Re-check rocker arms?? Maybe they need to be readjusted

Has the engine backfired after doing the cam swap? I have seen this pop the map sensor out of the back of the intake manifold. It really sounds like you have a big vacuum leak somewhere.

I haven't checked the rocker arms, but my understanding was that they were self adjusting. I installed them in the proper sequence and torqued them all to 22 ft lbs. per the specs.

As for the MAP sensor coming out, I haven't check that specifically, but I have checked all my vaccuum ports and cleaned all the electrical connections. I agree the symptoms are leaning toward that, but I can't find anything! Am I right, however, in assuming that it really shouldn't be a tuning issue?

reset the computer and see if it runs fine again for the first couple times...

jpkinerk wrote:I haven't checked the rocker arms, but my understanding was that they were self adjusting. I installed them in the proper sequence and torqued them all to 22 ft lbs. per the specs.

As for the MAP sensor coming out, I haven't check that specifically, but I have checked all my vaccuum ports and cleaned all the electrical connections. I agree the symptoms are leaning toward that, but I can't find anything! Am I right, however, in assuming that it really shouldn't be a tuning issue?

You're correct. Rocker arms are not adjustable.
Like Spence said. Reset the ECU and see if it idles. If not then you have something leaking vacuum. I assume you have a way of looking at values while the engine is running. This will tell you a lot of things. You can see if a sensor is stuck in one reading and if any actual values are way off.

Sounds like a plan. I've never reset the ECU before though, how exactly does one go about that?

jpkinerk wrote:Sounds like a plan. I've never reset the ECU before though, how exactly does one go about that?

It depends on what you have for a scanner. Some have a function to reset the learn tables. One simple way is to disconnect your battery for about 1 minute.

So I disconnected the battery overnight and nothing changed. However, I wouldn't lose the tune that was programmed on my ECU from the dyno by resetting the ECU, would I? Next is to triple check every sensor and vaccum hose, but I'm not optimistic. That said, I just can't beleive my existing tune wouldn't idle my new cam. The lift isn't that extreme.

No, you won't lose your tune. Only the stuff the ecu learns while running.

I have installed some pretty big lift cams and the engine would still idle. It would be erratic and usually ran rich, but it would idle well enough to work on the tune.
I assume you can start it and keep it running. If so, get someone to start it so that you can spray brake clean around the intake ports and other places that could leak vacuum. This will usually cause to engine to rev or bog down depending on what you spray. Its possible that you rolled an intake gasket out during install and it finally sucked out of the port when you were first running the engine. I know this can happen, because I've done it. I'm sure there is a simple explanation for your issue.

I would have never thought of checking the intake gaskets. Learn something new everyday. I will dig into it tomorrow and see what I find. Thanks again for the suggestions.

I had a problem with my initial tune I recieved. It was programmed for larger injectors than I specified. It would start then die. Start came from normal fuel enrichment sequence but then it would pull back fuel based on the injectors it thought it had. Just an oversight on the tuners part.

Jack

jpkinerk wrote:I would have never thought of checking the intake gaskets. Learn something new everyday. I will dig into it tomorrow and see what I find. Thanks again for the suggestions.

Did you find anything?

The holiday weekend (and an emergency motor mount repair on my DD) got in the way. I'm tearing into it tomorrow. Hopefully I'll find the problem and get my exhaust O2's in so I can get a tune Friday. I'm trying to get to LS Fest this coming weekend. Anyone going?

Hotrodz of Dallas wrote:

jpkinerk wrote:I would have never thought of checking the intake gaskets. Learn something new everyday. I will dig into it tomorrow and see what I find. Thanks again for the suggestions.

Did you find anything?

SUCCESS. So I pulled the intake off and the gaskets looked fine, however, they were pretty oil soaked and had sat off the car for quite some time this winter so I replaced them. I also noticed the fuel rail was not tightened down. Not sure if that would have mattered. Anyway, I torqued everything down to spec, started it up and it began to idle. The ECU is still learning so it tries to die at first, but each time I start it, things improve.

Now I'm wondering if it's OK to put some miles on it, or if I need a tune first. It previously (and still does) have a slightly rich tune for the track, but does anyone know if that's enough to compensate for a new cam? The lift is .605/.595 and 229/240 duration, intake/exhaust respectively. Thanks for all the comments, especially to HotRodz of Dallas!

it should be ok to drive around easy, but i wouldnt beat on it till you get it tuned. a cam upgrade is a very big change, if you were running a closed loop tune it might learn enough till its safe. if you have a wideband o2 gauge in the car you could use that to evaluate it and see how safe it might be.

I put almost exactly the same size cam in my 2004 GTO along with long tube headers. I drove it about a week before I could get it tuned. Other than trying to stall at times and running rich at idle, it drove ok.
Like sharkey said, don't beat on it at all, and you will be just fine.

Great. Thanks guys!